Decomposition of materials within a landfill produces landfill gas which contains methane. In some instances, the methane concentration is sufficient to warrant recovery of the landfill gas so that the methane can be used as a fuel. To increase the concentration of methane, a methane purification plant can be installed at the landfill.
The recovery of landfill gas and its purification requires a substantial investment for the construction of the necessary recovery and purification plant. Before making an investment of this magnitude, it is necessary to determine the methane potential of the landfill. The fact that a landfill is generating methane in economically recoverable quantities today is no guarantee that the landfill will continue to generate economically recoverable quantities of methane for a sufficient period to amortize the cost of the plant and to continue to defray the operating costs of the plant.
Unfortunately, very little is known about methane production in landfills and only theoretical, idealized approaches to establishing methane potential have been used. In one prior art process, a sample is taken from incoming refuse to a landfill and chemically analyzed. A stoichiometric equation is then used to approximate the methane yield. This approach does not provide any information as to the amount of methane already generated by the landfill nor does it show the rate at which the methane will be produced by the landfill over a period of time. Furthermore, this approach does not adequately take into account the changes in methane production and methane production rates found in various portions of the landfill.
Experimental laboratory studies have also been used in an effort to determine methane potential. Typically, in an experimental laboratory study, an effort is made to simulate a landfill. The flow rate of gas from the simulated fill is measured and the gas is chemically analyzed. From this, methane potential is estimated. Unfortunately, it has not been possible to accurately simulate actual landfill conditions. Moreover, the experimental studies are ordinarily conducted, out of necessity, over a relatively short period of time, such as six to eight months, whereas actual landfill gas production may occur over a ten to twenty-year period. There are indications that the balance between the microrganisms may be significantly different on these short-time tests than in a real landfill.
The problem of determining the methane potential is complicated because landfills are generally not homogeneous. For example, the composition of material within a landfill and the time of placement of the refuse in the landfill will vary. In addition, moisture content, permeability of the refuse, and air contamination of the landfill can affect methane generation, and these characteristics may vary from one location to another within the same landfill.